Air-cooled surface condenser



Jan. 22, 1963 H. ERTZ AIR-COOLED SURFACE CONDENSER 4 Sheets-Sheet 1 Filed Jan. 23, 1958 Jan. 22, 1963 H. ERTZ AIR-COOLED SURFACE CONDENSER 4 Sheets-Sheet 2 Filed Jan. 23, 1958 INVENTO/P flaw 5116' Jan. 22, 1963 H. ERTZ 3,074,478

AIR-COOLED SURFACE CONDENSER Filed Jan. 23, 1958 4 Sheets-Sheet 3 R I Q FIG. 3

INVENTOP 0 eda! $1,

011 4 Mala Jan. 22, 1963 H. ERTZ uwcoousn SURFACE CONDENSER 4 Sheets-Sheet 4 Filed Jan. 23, 1958 INVENIOP 0141 w. J YA?" 3,974,478 AlR-COGLED SURFAQE CQNDENSER Helmet Ertz, Bochum, Westphalia, Germany, assignor to EA- Lufthuhler Gesellschatt Bochum, Germay Filed .l" 23, 1953, filer. No. 719,545 Claims priority, application Germany Jan. 27, 1957 Claims. (Ql. 165-101) This invention relates to air-cooled surface condensers, and more specifically to an air-cooled surface condenser for multi-stage steam condensation and including several groups of cooling elements connected in parallel in relation to the steam to be condensed, which elements are each composed of a plurality of ribbed tubes connected up with common upper and lower end chambers. These cooling elements are arranged side by side in groups, each group of cooling elements being provided with one or more propeller blowers for circulating the cooling air. The cooling elements are inclined and their upper and lower end chambers are respectively connected to distribution and collecting conduits arranged substantially parallel to each other and at different heights.

in the known surface condensers of this type the steam to be condensed is fed through a number of distribution conduits to one of the groups of cooling elements connected in parallel in relation to the steam. The steam enters the ribbed tubes from higher actuated end chmnbers of the cooling elements and condenses in these tubes completely so that only the resultant condensate passes into lower situated end chambers and there enters a collecting conduit for the condensate.

Several rows of condenser tubes may be arranged successively in the direction in which the cooling air flows and are preferably constructed as ribbed tubes of elliptical cross section brushed on the outer side by a positively circulated or agitated current of cooling air sucked in from the atmosphere.

In the case of surface condensers of this type it is necessary, in order to obtain a condensation plant with a high degree of etficienc to provide special measures, for example adjustable regulating and throttling evices in the distribution conduits and chambers or a suitable construction of these conduits and chambers, by which measures the steam distribution to the individual cooling elements and the tu es thereof can always be accurately regulated in a complicated manner in the event of fluctuations in the steam supply. At the same time it is also necessary in many cases to provide measures for regulating the cooling air current, for example to use blowers with adjustable speed, with the result that the capital outlay for such a condenser plant is increased to an appreciable extent.

The object of the invention is to provide an air-cooled surface condenser which, while maintaining a high degree of efiicieney, can be adapted by simple means to strongly fluctuating quantities of waste steam and great differences in the temperature of the cooling air. This object is attained in that in a condenser with cooling elements arranged side by side in groups, the cooling elements of each group are connected through the intermediary of their lower situated end chamber to a common condensate collecting conduit of relatively large cross section, and are also connected by their higher located end chamber to a steam distribution conduit divided into front and rear sections in the direction of steam flow, the front section, which is preferably associated with a larger number of cooling elements than the rear section, being connected to a steam feed conduit and the rear section, which is associated with the remainder of the cooling elements, being connected to an Patented clan. 22, 1953 ice air suction device. By this arrangement therefore, only some of the cooling elements of each group are connected in parallel to the steam feed conduit. A partial condensation takes place in these cooling elements which extend at an incline in the direction of flow of the steam, so that through the lower end chambers of these cooling elements condensate and steam which is not yet condensed passes out into the condensate collecting conduit. This condensate collecting conduit has a considerably larger cross section than the conventional collecting conduits, but may be half as small than the mean cross section of the steam distribution conduit. The still uncondensed steam then passes from the condensate collecting conduit into the remaining cooling elements which have their upper end chambers connected .to the air suction device, flowing through these elements from the bottom to the top and being thereby also condensed. Owing to their inclined position, the condensate in these cooling elements, i.e. the last of each group, flows olf into the condensate collecting conduit in the opposite direction to the flow of steam. In these last cooling elements of each group therefore dephlegmatory condensation takes place. Due to the continuous transmission of heat from the steam to the condensate flowing in the opposite direction, the advantage is derived that the condensate cannot be undercooled under any circumstances. Even in the case of very low atmospheric temperatures the condensate can consequently never freeze. Another advantage of this arrangement is that, due to the dephlegmatory connection of the last cooling elements of each group, the condensate has a far greater heat content as compared with the known surface condensers. As this greater quantity of heat remaining in the cond nsate need not, in the case of the condenser proposed by the invention, be lead ofi by the cooling air, an improvement in the degree of efiiciency of the condensation is attained which is of considerable importance in the case of large plants. Due to the relatively high temperature of the condensate flowing oil, this only has a very low absorption capacity for air, so that practically complete degasification of the condensation product is attained. Corrosion through the oxygen of the air absorbed by the condensate cannot therefore occur in the condenser according to the invention. In the condensation plants heretofore known corrosion frequently takes place owing to the oxygen of the air being eagerly absorbed by the considerably cooler condensation product. The relatively high temperature of the condensation product flowing oil is an effective and sure protection against the freezing up of the condenser tubes in the case of low atmospheric temperatures, which can cause considerable operating trouble and damage to the condenser plant.

Owing to some of the cooling elements being dephlegrnatorily connected it is also possible to obtain in the steam distribution conduit a considerably higher vacuum than in the known condensers which are only parallel connected, so that a far greater percentage of the heat contained in the steam can be utilized. In a practical form of construction the cooling elements associated with that section of the steam distribution conduit which forms the rear section with respect to the direction of the steam flow, can be connected by their upper end chambers selectively to the steam feed or to the air suction device; Thus it is possible to utilize according to the actual quan tity of steam and/ or the temperature of the air, a variable number of cooling elements for the preand final condensation of the steam. The smaller the quantity of steam to be condensed and/or the lower the atmospheric temperature is, the smaller will be the number of cooling elements connected by their upper end chambers to the steam feed and the greater the number of cooling elements connected to the suction device. The more cooling elements of each group are dephlegmatorily connected up the higher will be the vacuum attainable in the steam distributing conduit, that is the greater will be the quantity of the heat content of the steam which can be utilized, for example, in a steam turbine. As compared with the conventional surface condensers having only parallel connected cooling elements, the utilizable drop in temperature can be increased in this manner by about to To vary the number of cooling elements connected respectively to the steam feed and to the air suction device, it is preferable to provide in the steam distribution conduit independently adjustable partitions which are situated between adjacent cooling elements connected with the rear section of the distribution conduit, which partitions are preferably constructed as disk-shaped shutofi flaps rotatable within the cross section of the distribution conduit. These shutolf flaps are of such cross-sectional shape that in open position they ofier the least possible resistance to the how of the steam in the distribution conduit.

According to another feature of the invention one or more non-adjustable propeller blowers are coordinated to the cooling elements permanently connected to the steam feed conduit, whereas at least one propeller blower with variable speed and/or adjustable blades is coordinated to the cooling elements connected to the air suction device. The cooling elements permanently connected to the steam feed conduit are consequently subjected to an air current of constant strength, whereas the air flow in the region of the dephlegmatorily connected cooling elements can be varied by changing the number of revolutions of the propeller blower or by adjusting the blower blades. It has been found that a control of the air flow only in the region of the dephlegmatorily connected cooling elements is amply sutticient for obtaining maximum utilization of the condenser so that simple and therefore inexpensive non-adjustable propeller blowers can be used for at least half the number of cooling elements.

The invention is diagrammatically illustrated by way of example in the accompanying drawings, in which:

FIG. 1 is a top plan view, partly in section, of two groups of cooling elements connected up with a common distribution conduit;

FIG. 2 is a section taken on line II-II of FIG. 1;

FIG. 3 is a longitudinal section of a group of cooling elements according to FIGS. 1 and 2; 1

FIG. 4 is a longitudinal section or a cooling element, and

FIG. Sis a section taken on line VV of FIG. 4.

FIGS. 1 and 2 show a condenser having cooling elements 1a-1f and 2a-2f arranged side by side in groups and which are shown on a larger scale in FIGS. 4 and 5. Each of the cooling elements is composed of a relatively large number of parallel, spaced ribbed tubes 3 of elliptical cross section. It is evident that the ribbed tubes 3 may be of some other cross-sectional shape than elliptical, for example they may be round or oval in cross section. The ends of the ribbed tubes 3 of each cooling element are connected to common upper and lower end chambers 4a and 4b. In the example illustrated in FIGS. 4 and 5 three rows of parallel tubes are arranged one behind the other in the direction of arrows x in which the cooling air flows. However, it is also possible to arrange two or more than three rows of tubes one behind the other in the direction of flow of the cooling air.

In the form of construction illustrated in FIGS. 1 to 3, each two oppositely arranged cooling elements of two parallel rows of cooling elements 1a-1f and 2a-2f are connected by means of their opposing upper end chambers 4a to a common steam distribution conduit 5, whereas the lower end chambers 4b of the cooling elements remote from each other are connected to condensate colthereto. Upper connection pieces 7 extending substantially over the entire length of the end chambers 4a serve for connecting the steam distribution conduit 5 to these end chambers, whereas the end chambers 4b of the cooling elements are connected with the condensate collecting conduits 6 and 6a by means of lower connection pieces 8 also extending substantially over the entire length of the end chambers 4b.

As shown in FIG. 2 the cooling elements la-lf and 2a-2f respectively of the parallel rows are arranged inclined to each other in root-shape and form the arms of an equilateral triangle. Between the two rows of cooling elements 1a-1f and 2a-2f propeller blowers 9 and 9a are arranged in series at a short distance apart in the longitudinal direction of the distribution conduit 5 and rotate in a substantially horizontal plane. The propeller blowers 9 and 9a are each provided with a separate driving motor 10 and, as can be seen from FIG. 2, are located substantially on the base of the equilateral tri angle formed by the cooling elements 1a-1j and 2a-2f. These propeller blowers 9 and 9a normally suck air from the atmosphere through a suction chamber open at the sides but not shown in the drawings, and force this air upwardly between the ribbed tubes 3 of the cooling elements in the direction of flow indicated by the arrows x. As shown in FIG. 2, the propeller blowers 9 and 9a are surrounded by a casing 11, and walls 12 extending between this casing 11 and the condensate collecting conduits 6 and 6a, respectively, serve to keep the flow of air within a space defined by the two rows of cooling elements.

In the forms of construction illustrated in the drawings the steam distribution conduit 5 is connected up with two groups each comprising six cooling elements 1a-1f and 212-2 two propeller blowers 9 and 9a being pro vided one behind the other at a slight distance apart in the longitudinal direction of the distribution conduit 5. It is evident, however, that a larger or smaller number of cooling elements can beconnected up with a steam distribution conduit 5, in which case a greater or smaller number of propeller blowers can be used if necessary. Deviating from the form of construction shown in the drawings, only one row of juxtaposed cooling elements can be connected to a steam distribution conduit 5. Also, the incline at which the cooling elements la-lf and Za-Zf extend with respect to the horizontal may be different from that indicated in the drawings.

The steam distribution conduit 5 has, as can be seen from FIGS. 1 and 3, a cross section tapering gradually in the direction y in which the steam flows, the reduction in cross section being proportionate to the quantities of steam led oif to the juxtaposed cooling elements. The cross section of the condensate collecting conduits 6 and 6a, on the other hand, increases from the two ends of each row of cooling elements, widening toward a discharge conduit 13 for the condensation product located substantially in the middle of each row. Taken on an average, however, the passage cross-sectional area of the steam distribution conduit 5 is considerably greater than the passage cross-sectional area of the two condensate collecting conduits 6 and 6a.

In the form of construction illustrated in FIGS. ,1 and 3 disk-shaped shutotf fiapsor valves 14, 14a and 14b are pivotally mounted in the distribution conduit 5 between the connection pieces 7 of the cooling elements lc-l and 20-21 connected with the rear and middle portions of the distribution conduit 5 respectively. These shutoff flaps or valves 14, 14a and 14b are rotatable independently of each other about substantially horizontal axes and are so dimensioned that they are capable of tightly closing the entire cross-sectional area of the distribution conduit 5. As can also be seen from FIGS. 1 and 3, the shutotf flaps 14, 14a and 14b are of flat stream lined cross section so that, when they are in open position, they offer only slight resistance to flow.

By selectively opening or closing the shutoif flaps 14, 14a and 146 the distribution conduit 5 can be divided at different points into a front conduit section 5a permanently connected to a steam feed conduit, not shown in the drawings, and a rear conduit section 5b connected to an air suction device 15. When the shutoff flaps 14, 14a and 14b are in the position illustrated in FIGS. 1 and 3, the cooling elements 1a-1d and 2a-2d are connected by their upper end chambers 4a facing each other to the steam feed conduit through the intermediary of the connection pieces 7 and the front section 5a of the distribution conduit 5, whereas the upper end chambers 4a of the cooling elements 1e, 1] and 2e, 2; are connected to the air suction device via the connection pieces 7 and the rear section 512 of the distribution conduit 5. The air suction device 15, which is preferably constructed as a steam ejector, is connected to the rear end of the distribution conduit 5 by means of a connecting pipe 17 fitted with a shutoff device 16.

In the condition illustrated in FIGS. 1 and 3 the steam flowing through the front conduit section 5a in the direction y passes through the connection pieces 7 into the cooling elements Ill-1d and 2a2d arranged at an incline to each other, and flows downwardly through these in the direction y In so doing the greater part of the steam fed to these cooling elements condenses and the resultant condensate flows off through the condensate collecting chambers 4b and the connection pieces 8 into the condensate collecting conduits 6 and 6a and thence through the discharge conduits 13. The steam which has not condensed in the cooling elements la-ld and Za-Zd flows through the condensate collecting conduits 6 and 6a in the direction y and enters the cooling elements 1e, 1 and 2e, 2f through the connection pieces 8 and flows through these elements in upward direction as indicated at y The remainder of the waste steam is condensed in these cooling elements, the condensate flowing off downwardly counter to the direction y of the steam flow into the condensate collecting conduits 6 and 6a and thence through the discharge conduits 13. The number of cooling elements connected up with the front section 5!! of the distribution conduit can be reduced to six by closing the flap 14 and at the same time opening the flap 14a, and it can be increased to ten by closing the flap 14b and at the same time opening the flap 14a. When a larger number of cooling elements are arranged side by side it is obvious that more shutoff flaps can be provided in the distribution conduit so that a. still greater change in the number of cooling elements directly connected to the steam feed conduit and to the air suction device respectively can be effected. As a rule, however, the number of cooling elements normally communicating with the front section of the distribution conduit 5 is chosen greater than the number of cooling elements dephlegrnatorily connected with the rear section of said conduit. The driving motor 10 of the propeller blower 9a coordinated to the cooling elements 1d-1f and 2d2f adapted for connection to the air suction device 15, is preferably of a type permitting infinitely variable speed regulation. In addition or instead thereof the blades of the propeller blower 9a may be adjustable in order to enable the quantity of the air current supplied by the blower to be regulated. The propeller lower 9 coordinated to the cooling elements 1a-1c and 212- permanently connected up with the steam feed conduit is, however, not regulatable but runs at a constant number or" revolutions. When employing a larger number of propeller lowers for each double row of cooling elements, in which case a correspondingly greater number of cooling elements can be connected by means of their facing end chambers 4a to the air suction device, two or more propeller blowers arranged one behind the other at the end of the double row directed towards the air suction device can be regulatable.

As can be seen from FIG. 3, several deflector or baiile plates 18 are arranged one behind the other at a distance' apart in the upper connection pieces 7 of the cooling elements Zia-1c and 2a-2c permanently connected up directly with the steam feed conduit. These bafile plates 18 are graded in height and project into the crosssectional area of the distribution conduit 5 a distance which increases in the direction of steam flow y but is nevertheless relatively slight. These battle plates 13 are intended to ensure a uniform supply of steam to all condenser tubes of the cooling elements 1a1c and 2a-2c.

Instead of the shutoff flaps 14, 14a and 14b illustrated in FIG. 3 it may in some cases be suficient to provide only a single stationary partition wall by which the steam distribution conduit 5 is permanently divided into a front section 5:: directly connected to the steam feed conduit and a rear section 5b connected to the air suction device 15 through the intermediary of the connection pipe 17. It will then be advisable to arrange the stationary partition wall between the upper connection pieces 7 of the cooling elements 1e, 1 and 2e, 2f connected up as the last two of each row to the rear section of the distribution conduit 5.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

I claim:

1. An air-cooled surface condenser comprising, in combination, an upper manifold; at least one lower condensate collecting manifold; a plurality of tubular cooling elements extending between said upper and said lower manifolds and communicating therewith, respectively; steam inlet means communicating with one end of said upper manifold for feeding steam to be condensed into said upper manifold; air suction means communicating with the other end of said upper manifold for discharging air therefrom; condensate outlet means communicating with said lower manifold for discharging condensate therefrom; and a plurality of partition means located in said upper manifold spaced from each other in longitudinal direction of said manifold, each of said partition means being movable between an active position in which said partition means extends transversely through said upper manifold to prevent flow of steam from said one to said other end of said manifold, and an inactive position in which said partition means permits substantially unrestricted flow of steam past said partition means, so that if one of said partition means is in said active position while the other of said partition means are in said inactive position thereof, said one partition means will divide said upper manifold into a front chamber between said one end of said manifold and said one partition means and a rear chamber between said one partition means and the other end of said manifold, so that steam fed through said steam inlet means passes from said front chamber through said cooling elements communieating therewith into said lower manifold while being condensed in part and the remaining steam being condensed as it passes from the lower manifold through the cooling elements communicating with said rear chamber into said rear chamber and so that the condensate formed in the cooling elements connected with said rear chamber flows in a direction opposite to the direction of steam flowing therethrough, whereby the influence of the steam on the condensate may be varied so as to avoid undercooling of the condensate.

2. An air-cooled surface condenser comprising, in combination, an upper manifold; at least one lower condensate collecting manifold; a plurality of tubular cooling elements extending between said upper and said lower manifolds and communicating therewith, respectively; steam inlet means communicating with one end of said upper manifold for feeding steam to be condensed into said upper manifold; air suction means communicating with the other end of said upper manifold for discharging air therefrom; condensate outlet means communicating with said lower manifold for discharging condensate therefrom; and a plurality of partition means located in said upper manifold spaced from each other in longitudinal direction of said manifold, each of said partition means being in the form of a disc pivotally mounted within said upper manifold and being movable between an active position in which said partition means extends transversely through said upper manifold to prevent flow of steam from said one to said other end of said manifold, and an inactive position in which saidpartition means permits substantially unrestricted flow of steam past said partition means, so that if one of said partition means is in said active position while the other of said partition means are in said inactive position] thereof, said one partition means will divide said upper manifold into a front chamber between said one end of said manifold and said one partition means and a rear'cha'mber between said one partition means and the other end of said manifold, so that steam fed through said steam inlet means passes from said front chamber through said cooling elements communicating therewith into said low-' er manifold while being condensed in part and the remaining steam being condensed as it passes from the lower manifold through the cooling elements communicating with said rear chamber into said rear chamber and so that the condensate formed in the cooling elements connected with said rear chamber flows in a direction opposite to the direction of steam flowing therethrough, whereby the influence of the steam on the condensate may be varied so as to avoid undercooling of the condensate.

3. An air-cooled surface condenser comprising, in combination, a condensate collecting manifold; a plurality of tubular cooling means for condensing steam therein and projecting spaced from each other upwardly from said condensate collecting manifold and communi-t eating with the lower ends thereof, respectively, with said manifold so that condensate formed from the condensing steam will flow downwardly through all said upwardly extending tubular cooling means; steam inlet means; air suction means; connecting means for connecting the upper end of at least one of said upwardly extending tubular cooling means to said steam inlet means for guiding steam in downward direction concurrently with the condensate fiowing downwardly therethrough,

for connecting the upper end of at least one other of said upwardly extending cooling means to said air suction means for guiding steam in upward direction in countercurrent to the condensate flowing downwardly therethrough, and for alternately connecting the upper end of each of the remaining upwardly extending tubular cooling means either to said steam inlet means for guiding steam in downward direction concurrently with the condensate flowing downwardly therethrough or to said suction means for guiding steam in'upward direction in countercurrent to the condensate flowing downwardly therethrough; and condensate outlet means connected to the condensate collecting manifold.

4. An arrangement as defined in claim 3 and in which said connecting means include an upper manifold with which the upper ends of all of said tubular cooling means communicate, in which said steam inlet means communicate with one end of said upper manifold for feeding steam to be condensed in said upper manifold, in which said air suction means communicate with the other end of said upper manifold for discharging air therefrom, and in which said connecting means further include means selectively spaced from said one end of said upper manifold for dividing the upper manifold into a front chamber communicating with said steam inlet means and into a rear chamber communicating with said air suction means.

5. An arrangement as defined in claim 3 and in which said connecting means include an upper manifold with which the upper ends of all of the tubular cooling means communicate, in which said steam inlet means communicate with one end of said upper manifold for feeding steam to be condensed insaid upper manifold, in which said air suction means communicate with the other end of said upper manifold for discharging air therefrom, and in which said connecting means further include partition means extending transversely through said upper manifold selectively spaced from said one end thereof.

7 References Cited in the file of this patent UNITED STATES PATENTS 1,634,903 Hodgkinson July 5, 1927 1,710,910 Whitney Apr. 30, 1929 1,864,286 Walker June 21, 1932 2,107,478- Happel Feb. 8, 1938 2,217,410 Howard -e Oct. 8, 1940 2,768,814 Frey et al Oct. 30, 1956 FOREIGN PATENTS 689,080 France Sept. 2, 1930 

1. AN AIR-COOLED SURFACE CONDENSER COMPRISING, IN COMBINATION, AN UPPER MANIFOLD; AT LEAST ONE LOWER CONDENSATE COLLECTING MANIFOLD; A PLURALITY OF TUBULAR COOLING ELEMENTS EXTENDING BETWEEN SAID UPPER AND SAID LOWER MANIFOLDS AND COMMUNICATING THEREWITH, RESPECTIVELY; STEAM INLET MEANS COMMUNICATING WITH ONE END OF SAID UPPER MANIFOLD FOR FEEDING STEAM TO BE CONDENSED INTO SAID UPPER MANIFOLD; AIR SUCTION MEANS COMMUNICATING WITH THE OTHER END OF SAID UPPER MANIFOLD FOR DISCHARGING AIR THEREFORM; CONDENSATE OUTLET MEANS COMMUNICATING WITH SAID LOWER MANIFOLD FOR DISCHARGING CONDENSATE THEREFROM; AND A PLURALITY OF PARTITION MEANS LOCATED IN SAID UPPER MANIFOLD SPACED FROM EACH OTHER IN LONGITUDINAL DIRECTION OF SAID MANIFOLD, EACH OF SAID PARTITION MEANS BEING MOVABLE BETWEEN AN ACTIVE POSITION IN WHICH SAID PARTITION MEANS EXTENDS TRANSVERSELY THROUGH SAID UPPER MANIFOLD TO PREVENT FLOW OF STEAM FROM SAID ONE TO SAID OTHER END OF SAID MANIFOLD, AND AN INACTIVE POSITION IN WHICH SAID PARTITION MEANS PERMITS SUBSTANTIALLY UNRESTRICTED FLOW OF STEAM PAST SAID PARTITION MEANS, SO THAT IF ONE OF SAID PARTITION MEANS IS IN SAID ACTIVE POSITION WHILE THE OTHER OF SAID PARTITION MEANS ARE IN SAID INACTIVE POSITION THEREOF, SAID ONE PARTITION MEANS WILL DIVIDE SAID UPPER MANIFOLD INTO A FRONT CHAMBER BETWEEN SAID ONE END OF SAID MANIFOLD AND SAID ONE PARTITION MEANS AND A REAR CHAMBER BETWEEN SAID ONE PARTITION MEANS AND THE OTHER END OF SAID MANIFOLD, SO THAT STEAM FED THROUGH SAID STEAM INLET MEANS PASSES FROM SAID FRONT CHAMBER THROUGH SAID COOLING ELEMENTS COMMUNICATING THEREWITH INTO SAID LOWER MANIFOLD WHILE BEING CONDENSED IN PART AND THE REMAINING STEAM BEING CONDENSED AS IT PASSES FROM THE LOWER MANIFOLD THROUGH THE COOLING ELEMENTS COMMUNICATING WITH SAID REAR CHAMBER INTO SAID REAR CHAMBER AND SO THAT THE CONDENSATE FORMED IN THE COOLING ELEMENTS CONNECTED WITH SAID REAR CHAMBER FLOWS IN A DIRECTION OPPOSITE TO THE DIRECTION OF STEAM FLOWING THERETHROUGH, WHEREBY THE INFLUENCE OF THE STEAM ON THE CONDENSATE MAY BE VARIED SO AS TO AVOID UNDERCOOLING OF THE CONDENSATE. 